Reproduction of sound records



KL SCHWARZ REPRODUCTION OF SOUND RECORDS Sept. 21, 1937.

Filed July 2, 1955 INVENTQR KARL SCH ARZ BY 7 M 1 ATTORNEY I PatentedSept. 21, 1937 1 y UNITED ST TE-s PATENTUOFFICE REPRODUCTION OFsounnnnoonns t Karl 'Sc hwarz, Berlin, Germany, assignor to. I i 1Klangfilm G. in. b. H., Berlin, Germany, a corporation of Germany 10fing..electrical currents.

1 An apparatus has beenprovidedfor reproducing sound records whichhavethe positive and negative halves of the sound waves recorded onseparatetracksf Inthis apparatus threelenses 15 are mountedbetweeni thefilm strip and the photoelectric cells for imaging the two soundtrackson the. cathodes of the pl'ioto-electric cells connected push-pull.(inphase opposition).. I

, The presentinventionis concerned with an ar- 'zo rangementginrwhichthe two photocells are mounted comparatively close to and back of thefilm strip in a manner somewhat similar to that suggested in connectionwith the use of a single J photocell for reproducing a single tracksound 25 record. If an attemptis made to reproduce a 1 photographicsound track in whichthe positive t and the negative halves have beenrecorded separately by means of the prior artreproducer adapted tohandle single track sound records, difficulty 30 in securing a properdistribution of the film modulated light is encountered. In accordancewith 3 this invention this difficulty is avoided by the provision of areflecting barriermounted in proximity to the film path and interposedbetween the film 'and light sensitive cell;

The invention will be better understood from t the following descriptionwhen considered in connection with the accompanying drawing, and'itsscope will be pointed out in the appended claims.

Cir:

40 Referring to the drawing,

Fig. 1 illustrates a positive sound record of the variable area type,

Fig. 2 illustratesan arrangement wherein the photocell is mounted inclose proximity to the 50 light.

I Fig. 1 illustrates a sound record having variable area sound tracksIll and I l of the positive andthe negative halves of the sound wavesspaced from one another. This film strip is assumed to represent apositive ready to be used and is blackened Application July 2, 1935,Serial No. 29,437

Germany September 22, 1934 1. 2 Claims. (01. ire-100.3

in those portions which are shaded in Fig. 1. However, it will beunderstoodthat the invention will be found equally -useful in the caseof films in which the positive "and negative half cycle-sound tracks'arerecorded :by the variable 5 density method. Y t t The production of aslenderlineof light for re-' producing films of this kind is efiected'in the same way as in the case of standard sound films bearing asingle-track sound record. 'Ihus by the aid'of an objective l2, theimage' of an illuminated slit l3 is thrown upon thefilm as' shown inFig.2; The image of this slit [3 isassumed to'liebetween lines A and Bon the film strip. For a proper 'ap-' p'reciation of the particularproblemarising in'the reproductionpf a twin-trackrecord such asth'atillustrated by Fig.1, it is-necessary 'toconsider under what particularcircumstances an imageof slit I3 is produced upon the filmstrip.Fundamentally speaking, ofcourse', this .picture is obtained in asimilar manner as any other optical image. Thus light rays issuing froma definite point P1 of the slit l3 are focussed at a definite point ofthe image P1. The marginal rays of the ray pencils imaging the two lastmentioned points are traced in the drawing, for the sake of greaterclarity of representation, only between the lens l2 and the film, theimage of point P2 being denote by P2, and the image of point P3 by P3.

These paths of the light rays posteriorly of the film makes it clearthat, in the case of a pick-up of a double-track sound record it ispossible to mount two photocells or a twin photo-electric cell directlyin the rear of the film. If an attempt is made to mount atwin photocellspaced from the film as shown in Fig. 2 it will benoticed that the lightrays which have imaged point P3 of the track I 0 will cross the rayswhich image point P2 a short distance behind the film. In other words,if a twin photocell were mounted at close proximity to and posteriorlyofthe film it would not be feasible at] all to direct the light rayscoming from the track l0 exclusively to one of the two cathodes l 4, I5and the light rays coming from sound track I I exclusively onto therespective other cathode. However, this is required if the photocellcurrents due to the light transmitted through the film are to beproperly combined.

In the reproduction of ordinary single-track sound records this problemdoes not arise because all that has to be done in this instance is totake care so that all of the light transmitted across the film stripwill actually be caused to impinge upon the cathodes of the photocell.In other words, in scanning single-track sound records there are nodifficulties in disposing the single photocell then necessaryimmediately in the rear of the film such as has been done in a greatmany forms of construction known in the prior art.

In order that a similarly simple arrangement may be carried intopractice in the reproduction of twin-track sound records and that thecomplicated construction comprising three distinct lenses heretoforeproposed may be avoided, a"

bilaterally reflecting body extending from a point at close proximity tothe film, to the twin photocell and the two separate photocell units isprovided. An arrangement of this kind is shown in Figs. 3a and 3b inplan and elevation covering the case of a double photocell. In order tographically show that the problem discussed by reference to Fig. 2 isnow actually solved, the light rays have been traced in Fig. 3a whichoriginate from the slit image pointsPz and P3. As can be seen from thisillustration, one of the two marginal rays is reflected from thebilaterally reflective body I 6 and thus reaches the right photocellcathode. In a similar fashion, the rays I1 and I8 inside the pencil ofrays pertaining to image point P2 ,will be reflected from the body l6.Those rays which are positioned so close to the line of symmetry of theray pencil which issues from point P2 that they will'no longer strikethe reflector body I6 will still not reach the wrong photo-electriccell; and in order that this may be so, the distance between the twocathode surfaces within the photo-electric cell must be properly chosen.Inside the plane of the drawing Fig. 3b in which the stationary glide orfeed path for the film, similarly as in Fig. 3a, is

designated by [9 and in which also the shape of reflective body I6 ismore clearly recognizable, there occurs no reflection of the light raysfrom the reflecting body. The marginal rays of both ray pencils, whichby the Way, register or coincide in this View, are shown by the brokenlines in Fig, 3b.

If the bilaterally reflecting body as shown in Fig. 4 is made larger inwidth towards the photocell so that it assumes the form of a wedge 20,the.inter-cathodedistance in the cell designated by d in Fig. 3a can bediminished.

Fig. 5 shows an arrangement which corresponds to that in Fig. 3, thoughcomprising two separate photo-electric cells. In the light of whatprecedes, further discussion of this embodiment is unnecessary.

I claim:

1; In a device for reproducing sound from a record having the positiveand negative halfcycles recorded in tracks spaced from one another, thecombination of means for defining a film path, a light sensitive devicehaving two light-sensitive electrodes, and a bilaterally reflectingmember extending between said path and said device for directing lightfrom the respective half-cycle tracks to the corresponding elec trodes.

2. In a device for reproducing sound from a record having the positiveand negative halfcycles recorded in tracks spaced from one another, thecombination of means for defining a fllm path, a light sensitive devicehaving two light-sensitive electrodes, and a bilaterallyreflectingmember located intermediate said tracks and extending betweensaid path and said device for directing light from the respectivehalfcycle tracks to the corresponding electrodes.

KARL SCHWARZ.

